2-Amino-2-methyl-1-propanol regulated triethylenetetramine-based nonaqueous absorbents for solid-liquid phase-change CO2 capture: Formation of crystalline powder products and mechanism analysis

Solid-liquid phase-change absorbents (SLPCAs) have a great potential to reduce the energy consumption of CO 2 capture. The main issue in the practical application of SLPCAs is the difficulty in the phase separation of gelatinous solid products. In this study, 2-amino-2-methyl-1-propanol (AMP) was used as a regulator to tune the physical form of the solid products of triethylenetetramine (TETA)-based SLPCAs. Experimental results showed that the AMP-regulated TETA-based SLPCAs successfully avoided the formation of gelatinous products (viscosity up to more than 1000 mPa·s) and yielded easily separated crystalline powders. Among the investigated SLPCAs, TETA/AMP/ N -methyl-2-pyrrolidone (NMP) (TETA:AMP = 2:8, 1 M) exhibited the best CO 2 capture performance with a high CO 2 loading of 0.94 mol·mol −1 and a high regeneration efficiency of 84.14 %. XRD, FT-IR and 13 C NMR analyses indicated that TETA/AMP/NMP absorbed CO 2 to form highly polar carbamate species and protonated amines, which could break the original assimilation state of the SLPCA system; thus, the polar products precipitated out from less polar NMP, leading to a phase change. The theoretical calculations revealed that in the absence of AMP, the TETA-derived products had a tendency to form gelatinous aggregation with large amounts of hydrogen bonds; with the introduction of AMP, the AMP-derived products tended to combine with the TETA-derived products via strong electrostatic attraction and Van der Waals force and effectively inhibited the aggregation formation. Since there was only one hydrogen bond forming between the AMP- and TETA-derived product molecules, the amount of hydrogen bonds was significantly reduced. Eventually, the TETA/AMP/NMP SLPCA avoided the formation of gelatinous products and yielded crystalline powder products.